Magnets are used in many fields of technology to perform various operations, such as to control motion, to switch electrical circuits and to move objects. A magnet is typically provided with a certain functionality to change its magnetic state. A magnet may comprise, for example, a coil which produces a magnetic field that is dependent on the amount and the direction of the electric current supplied to the coil. The coil may be used alone, or it can be combined with a permanent magnet, whereby the coil is used to increase or decrease the magnetic field produced by the permanent magnet. Alternatively, a magnet may comprise a movable part, the position of which determines the magnetic state of the magnet. The movable part, which comprises a permanent magnet, is moved relative to a body of the magnet, for example, with a magnetic force produced by a coil that is arranged to encircle the movable part.
An example of a magnet that comprises a movable part for changing the magnetic state of the magnet is disclosed in the document WO 2012/160262. The magnet of the document WO 2012/160262 is a so-called bi-stable magnet, wherein the movable part, which comprises a permanent magnet, is arranged to be movable relative to a body of the magnet between two stable positions. In the first position, the movable part is in contact with the body, whereby the magnetic flux generated by the permanent magnet may be directed through the body to an object to be attached. In the second position, the movable part is separated from the body so that the flow of the magnetic flux in the body is significantly reduced and thus the holding force of the magnet is negligible. The body of the magnet comprises a coil that is arranged around the movable part. The movable part is moved between the two positions by supplying a sufficient amount of electric current through the coil in a suitable direction.
A problem associated with the magnet of the document WO 2012/160262 relates to the bi-stability of the magnet. The magnet can only be in either of its two states and the state of the magnet is changed by moving the movable part from one stable position to the other. Consequently, the holding force of the magnet that is dependent on the position of the movable part has only two fixed values. In other words, the holding force of the magnet of the document WO 2012/160262 cannot be adjusted, which reduces the applicability of the magnet.
Another problem associated with the magnet of the document WO 2012/160262 relates to the second position of the movable part, i.e. to the position wherein the movable part is not in contact with the body. In order to make sure that the movable part stays in its second position, either electric current must constantly be supplied to the coil, or the magnet must be provided with springs or other suitable means to push the movable part towards the second position. In the first case, a disadvantage is the power consumption of the coil, whereas in the second case, a disadvantage is the complicated structure, which may easily be damaged, thus resulting in a malfunction of the magnet.